The need for the control of, inter alia, highway, railway, industrial and rapid transit noise in urban areas is well recognized, and sound barriers for this purpose are widely utilized.
One common sound barrier includes a plurality of vertically-extending, ground-mounted metal I-beam columns, having interleaved therebetween a plurality of wall panels. Exemplary in this regard is the sound barrier disclosed in U.S. Pat. No. 4,325,457 (Docherty et al.), issued Apr. 20, 1982, which utilizes relatively light-weight cementitious panels. This sound barrier is known to be relatively inexpensive to manufacture and erect, and to provide acceptable levels of noise control. However, its wall panels, being cementitious, are completely opaque, and thereby block the transmission of light and the view of persons in the vicinity, which in certain circumstances can be undesirable, inter alia, from the standpoints of aesthetics and safety.
Large sheets of glass could, in principle, be used as wall panels in sound barriers. However, the cost of suitable glass, to wit, of sufficient strength to serve such purpose, is relatively high. Further, glass suffers from a propensity to shatter into sharp shards upon impact, thereby rendering it difficult and dangerous to work with, and unsuitable for use in situations wherein impacts could be expected, such as, for example, alongside highways.
Large sheets of synthetic transparent or translucent material that does not suffer from a propensity to shatter into sharp shards, such as acrylic or polycarbonate, are, in principle, also available for use as wall panels in sound barriers. However, not only is the cost of such materials relatively high, but, by virtue, inter alia, of the thermal expansion properties of available synthetic materials, it can be difficult to secure panels constructed therefrom to suitable supports. Moreover, supports that are constructed to accommodate panel movement during thermal expansion and contraction tend to increase the risk of withdrawal of the panels from their supports when the panels bow under wind or other loading; stiffening the panels against bowing by increasing their thickness adds detrimentally to cost and can impair light transmission, and similarly, increasing the size and complexity of the supports adds detrimentally to cost and can detract from the aesthetics of the wall. For reasons such as these, the use of transparent or translucent sheets of synthetic materials as wall panel components in sound barriers has been limited.